Mesothelin CAR T-cells secreting anti-FAP/anti-CD3 molecules efficiently target pancreatic adenocarcinoma and its stroma

PURPOSE

Targeting solid tumors with CAR T-cells remains challenging due to heterogenous target antigen expression, antigen escape, and the immunosuppressive tumor microenvironment (TME). Pancreatic cancer is characterized by a thick stroma generated by cancer-associated fibroblasts (CAFs), which may contribute to the limited efficacy of mesothelin-directed CAR T-cells in early-phase clinical trials. To provide a more favorable TME for CAR T-cells to target pancreatic ductal adenocarcinoma (PDAC), we generated T-cells with an anti-mesothelin CAR and a secreted T-cell-engaging molecule (TEAM) that targets CAFs through fibroblast activation protein (FAP) and engages T-cells through CD3 (termed mesoFAP CAR-TEAM cells).

EXPERIMENTAL DESIGN

Using a suite of in vitro, in vivo, and ex vivo patient-derived models containing cancer cells and CAFs, we examined the ability of mesoFAP CAR-TEAM cells to target PDAC cells and CAFs within the TME. We developed and used patient-derived ex vivo models including patient-derived organoids with patient-matched CAFs and patient-derived organotypic tumor spheroids (PDOTS).

RESULTS

We demonstrated specific and significant binding of the TEAM to its respective antigens (CD3 and FAP) when released from mesothelin-targeting CAR T cells, leading to T cell activation and cytotoxicity of the target cell. MesoFAP CAR-TEAM cells were superior in eliminating PDAC and CAFs compared to T cells engineered to target either antigen alone in our ex-vivo patient-derived models and in mouse models of PDAC with primary or metastatic liver tumors.

CONCLUSIONS

CAR-TEAM cells enable modification of tumor stroma, leading to increased elimination of PDAC tumors. This approach represents a promising treatment option for pancreatic cancer.

Extracellular vesicle analysis of plasma allows differential diagnosis of atypical pancreatic serous cystadenoma

Increased use of cross-sectional imaging has resulted in frequent detection of incidental cystic pancreatic lesions. Serous cystadenomas (SCAs) are benign cysts that do not require surgical intervention unless symptomatic. Unfortunately, up to half of SCAs do not have typical imaging findings ("atypical SCAs"), overlap with potentially malignant precursor lesions, and thus pose a diagnostic challenge. We tested whether the analysis of circulating extracellular vesicle (EV) biomarkers using a digital EV screening technology (DEST) could enhance the discrimination of cystic pancreatic lesions and avoid unnecessary surgical intervention in these atypical SCAs. Analysis of 25 different protein biomarkers in plasma EV from 68 patients identified a putative biomarker signature of Das-1, Vimentin, Chromogranin A, and CAIX with high discriminatory power (AUC of 0.99). Analysis of plasma EV for multiplexed markers may thus be helpful in clinical decision-making.

Single-nucleus and spatial transcriptome profiling of pancreatic cancer identifies multicellular dynamics associated with neoadjuvant treatment

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal and treatment-refractory cancer. Molecular stratification in pancreatic cancer remains rudimentary and does not yet inform clinical management or therapeutic development. Here, we construct a high-resolution molecular landscape of the cellular subtypes and spatial communities that compose PDAC using single-nucleus RNA sequencing and whole-transcriptome digital spatial profiling (DSP) of 43 primary PDAC tumor specimens that either received neoadjuvant therapy or were treatment naive. We uncovered recurrent expression programs across malignant cells and fibroblasts, including a newly identified neural-like progenitor malignant cell program that was enriched after chemotherapy and radiotherapy and associated with poor prognosis in independent cohorts. Integrating spatial and cellular profiles revealed three multicellular communities with distinct contributions from malignant, fibroblast and immune subtypes: classical, squamoid-basaloid and treatment enriched. Our refined molecular and cellular taxonomy can provide a framework for stratification in clinical trials and serve as a roadmap for therapeutic targeting of specific cellular phenotypes and multicellular interactions.

Abstract SY12-04: Multicellular spatial community featuring a novel neuronal-like malignant phenotype is enriched in pancreatic cancer after neoadjuvant chemotherapy and radiotherapy

Pancreatic ductal adenocarcinoma (PDAC) is projected to be the second leading cause of cancer mortality in the United States by 2030. Given that resistance to cytotoxic therapy is pervasive, there is a critical need to elucidate salient gene expression programs and spatial relationships among malignant and stromal cells in the tumor microenvironment (TME), particularly in residual disease. We developed and applied a single-nucleus RNA-seq (snRNA-seq) technique to 43 banked frozen primary PDAC specimens that either received neoadjuvant therapy (n=25) or were treatment-naïve (n=18). We discovered expression programs across malignant cell and fibroblast profiles that formed the basis for a refined molecular taxonomy, including a novel neural-like progenitor (NRP) malignant program enriched with neoadjuvant treatment in tumors and organoids, and associated with the worst prognosis in bulk profiles from independent cohorts.

To elucidate how neoadjuvant treatment and cancer cell- and fibroblast-intrinsic programs modulate the composition of multicellular neighborhoods, we performed spatial profiling with the GeoMx[1] platform (NanoString) on 21 formalin-fixed paraffin-embedded sections using the human whole transcriptome atlas (WTA). Each tumor showed intra-tumoral heterogeneity in tissue architecture and regions of interest (ROIs) with diverse patterns of neoplastic cells, cancer-associated fibroblasts (CAFs), and immune cells were selected for profiling. We deconvolved the WTA data with our snRNA-seq cell type signatures and mapped expression programs onto the tumor architecture to reveal three distinct multicellular neighborhoods, which we annotated as classical, squamoid-basaloid, and treatment-enriched. The observed enrichment in post-treatment residual disease of multiple spatially-defined receptor-ligand interactions and a neighborhood featuring the NRP program, neurotropic CAF program, and CD8+ T cells may open new therapeutic opportunities.

Next, we mapped malignant/CAF programs and immune cell subsets at single-cell spatial resolution by performing spatial molecular imaging (SMI[2]; NanoString CosMx) using a panel of 960 RNA targets on a subset of seven tumors (2 untreated, 5 treated) and captured over 200,000 cells with an average of more than 450 transcripts detected per cell. Correlating ROIs from whole-transcriptome DSP to matched fields of view in kiloplex SMI enabled further dissection of PDAC architecture and treatment-associated remodeling of cell type distributions and receptor-ligand interactions.

Ongoing functional studies have begun to elucidate the key regulatory elements underlying the distinct treatment-associated NRP malignant program and its interactions with the TME. Overall, the complementary combination of snRNA-seq, whole-transcriptome DSP, and kiloplex SMI provides a high-resolution molecular framework that can be harnessed to augment precision oncology efforts in pancreatic cancer.

[1] GeoMx DSP is for Research Use Only and not for use in diagnostic procedures. [2] CosMx SMI is for Research Use Only and not for use in diagnostic procedures.

Citation Format: William L. Hwang, Karthik A. Jagadeesh, Jimmy A. Guo, Hannah I. Hoffman, Carina Shiau, Jennifer Su, Payman Yadollahpour, Jason W. Reeves, Youngmi Kim, Sean Kim, Mark Gregory, Prajan Divakar, Eric Miller, Michael Rhodes, Sarah Warren, Erroll Rueckert, Kit Fuhrman, Daniel R. Zollinger, Robin Fropf, Joseph M. Beechem, Arnav Mehta, Toni Delorey, Cristin McCabe, Jaimie L. Barth, Piotr Zelga, Cristina R. Ferrone, Motaz Qadan, Keith D. Lillemoe, Rakesh K. Jain, Jennifer Y. Wo, Theodore S. Hong, Ramnik Xavier, Orit Rozenblatt-Rosen, Andrew J. Aguirre, Carlos Fernandez-Del Castillo, Andrew S. Liss, Mari Mino-Kenudson, David T. Ting, Tyler Jacks, Aviv Regev. Multicellular spatial community featuring a novel neuronal-like malignant phenotype is enriched in pancreatic cancer after neoadjuvant chemotherapy and radiotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr SY12-04.

Single-EV analysis (sEVA) of mutated proteins allows detection of stage 1 pancreatic cancer

Tumor cell-derived extracellular vesicles (EVs) are being explored as circulating biomarkers, but it is unclear whether bulk measurements will allow early cancer detection. We hypothesized that a single-EV analysis (sEVA) technique could potentially improve diagnostic accuracy. Using pancreatic cancer (PDAC), we analyzed the composition of putative cancer markers in 11 model lines. In parental PDAC cells positive for KRASmut and/or P53mut proteins, only ~40% of EVs were also positive. In a blinded study involving 16 patients with surgically proven stage 1 PDAC, KRASmut and P53mut protein was detectable at much lower levels, generally in <0.1% of vesicles. These vesicles were detectable by the new sEVA approach in 15 of the 16 patients. Using a modeling approach, we estimate that the current PDAC detection limit is at ~0.1-cm3 tumor volume, below clinical imaging capabilities. These findings establish the potential for sEVA for early cancer detection.

Mutant GNAS limits tumor aggressiveness in established pancreatic cancer via antagonizing the KRAS-pathway

BACKGROUND

Mutations in GNAS drive pancreatic tumorigenesis and frequently occur in intraductal papillary mucinous neoplasm (IPMN); however, their value as a therapeutic target is yet to be determined. This study aimed at evaluating the involvement of mutant GNAS in tumor aggressiveness in established pancreatic cancer.

METHODS

CRISPR/Cas9-mediated GNAS R201H silencing was performed using human primary IPMN-associated pancreatic cancer cells. The role of oncogenic GNAS in tumor maintenance was evaluated by conducting cell culture and xenograft experiments, and western blotting and transcriptome analyses were performed to uncover GNAS-driven signatures.

RESULTS

Xenografts of GNAS wild-type cells were characterized by a higher Ki-67 labeling index relative to GNAS-mutant cells. Phenotypic alterations in the GNAS wild-type tumors resulted in a significant reduction in mucin production accompanied by solid with massive stromal components. Transcriptional profiling suggested an apparent conflict of mutant GNAS with KRAS signaling. A significantly higher Notch intercellular domain (NICD) was observed in the nuclear fraction of GNAS wild-type cells. Meanwhile, inhibition of protein kinase A (PKA) induced NICD in GNAS-mutant IPMN cells, suggesting that NOTCH signaling is negatively regulated by the GNAS-PKA pathway. GNAS wild-type cells were characterized by a significant invasive property relative to GNAS-mutant cells, which was mediated through the NOTCH regulatory pathway.

CONCLUSIONS

Oncogenic GNAS induces mucin production, not only via MUC2 but also via MUC5AC/B, which may enlarge cystic lesions in the pancreas. The mutation may also limit tumor aggressiveness by attenuating NOTCH signaling; therefore, such tumor-suppressing effects must be considered when therapeutically inhibiting the GNAS pathway.

T cells armed with C-X-C chemokine receptor type 6 enhance adoptive cell therapy for pancreatic tumours

The efficacy of adoptive cell therapy for solid tumours is hampered by the poor accumulation of the transferred T cells in tumour tissue. Here, we show that forced expression of C-X-C chemokine receptor type 6 (whose ligand is highly expressed by human and murine pancreatic cancer cells and tumour-infiltrating immune cells) in antigen-specific T cells enhanced the recognition and lysis of pancreatic cancer cells and the efficacy of adoptive cell therapy for pancreatic cancer. In mice with subcutaneous pancreatic tumours treated with T cells with either a transgenic T-cell receptor or a murine chimeric antigen receptor targeting the tumour-associated antigen epithelial cell adhesion molecule, and in mice with orthotopic pancreatic tumours or patient-derived xenografts treated with T cells expressing a chimeric antigen receptor targeting mesothelin, the T cells exhibited enhanced intratumoral accumulation, exerted sustained anti-tumoral activity and prolonged animal survival only when co-expressing C-X-C chemokine receptor type 6. Arming tumour-specific T cells with tumour-specific chemokine receptors may represent a promising strategy for the realization of adoptive cell therapy for solid tumours.

Screening and Validation of Molecular Targeted Radiosensitizers

The development of molecular targeted drugs with radiation and chemotherapy are critically important for improving the outcomes of patients with hard-to-treat, potentially curable cancers. However, too many preclinical studies have not translated into successful radiation oncology trials. Major contributing factors to this insufficiency include poor reproducibility of preclinical data, inadequate preclinical modeling of inter-tumoral genomic heterogeneity that influences treatment sensitivity in the clinic, and a reliance on tumor growth delay instead of local control (TCD50) endpoints. There exists an urgent need to overcome these barriers to facilitate successful clinical translation of targeted radiosensitizers. To this end, we have employed 3D cell culture assays to better model tumor behavior in vivo. Examples of successful prediction of in vivo effects with these 3D assays include radiosensitization of head and neck cancers by inhibiting epidermal growth factor receptor or focal adhesion kinase signaling, and radioresistance associated with oncogenic mutation of KRAS. To address the issue of tumor heterogeneity we leveraged institutional resources that allow high-throughput 3D screening of radiation combinations with small molecule inhibitors across genomically characterized cell lines from lung, head and neck, and pancreatic cancers. This high-throughput screen is expected to uncover genomic biomarkers that will inform the successful clinical translation of targeted agents from the NCI CTEP portfolio and other sources. Screening "hits" need to be subjected to refinement studies that include clonogenic assays, addition of disease-specific chemotherapeutics, target/biomarker validation, and integration of patient-derived tumor models. The chemoradiosensitizing activities of the most promising drugs should be confirmed in TCD50 assays in xenograft models with/without relevant biomarker and utilizing clinically relevant radiation fractionation. We predict that appropriately validated and biomarker-directed targeted therapies will have a higher likelihood than past efforts to be successfully incorporated into the standard management of hard-to-treat tumors.

Abstract 94: Multi-compartment reprogramming and spatially-resolved interactions in frozen pancreatic cancer with and without neoadjuvant chemotherapy and radiotherapy at single-cell resolution

A molecular classification of pancreatic ductal adenocarcinoma (PDAC) that informs clinical management remains elusive. Previously identified bulk expression subtypes in the untreated setting were influenced by contaminating stroma whereas single cell RNA-seq (scRNA-seq) of fresh tumors under-represented key cell types. Two consensus subtypes have arisen from these prior efforts: (1) classical-like, and (2) basal-like. Basal-like tumors were associated with worse survival in the metastatic setting but attempts to refine this binary classification have failed to further stratify patient survival. Here, we developed a robust single-nucleus RNA-seq (snRNA-seq) technique for banked frozen PDAC specimens and studied a cohort of untreated resected primary tumors (n ~ 20). Gene expression programs learned across malignant cell and cancer-associated fibroblast (CAF) profiles uncovered a clinically-relevant molecular taxonomy with improved prognostic stratification compared to prior classifications. Digital spatial profiling revealed an association between malignant cells expressing basal-like programs and greater immune infiltration with relatively fewer macrophages, whereas those exhibiting classical-like programs were linked to inflammatory CAFs and macrophage-predominant microniches. Recent clinical trials have supported the increasing adoption of neoadjuvant therapy to aggressively address the risk of micro-metastatic spread and to circumvent concerns of treatment tolerance in the postoperative setting. There is an urgent need to understand how preoperative treatment impacts residual tumor cells and their interactions with other cell types in the tumor microenvironment to identify additional therapeutic vulnerabilities that can be exploited. Towards this end, we performed snRNA-seq on an unmatched cohort of neoadjuvant-treated resected primary tumors (n ~ 25) with most cases involving FOLFIRINOX chemotherapy followed by chemoradiation. Remarkably, the quality of single-nucleus mRNA profiles was comparable between heavily pre-treated and untreated specimens. We identified differentially expressed genes between treated and untreated samples to infer cell-type specific reprogramming in the residual tumor. This analysis revealed that in the neoadjuvant treatment context, there was lower expression of classical-like phenotypes in malignant cells in favor of basal-like phenotypes associated with TNF-NFkB and interferon signaling as well as the presence of novel acinar and neuroendocrine classical-like states. Our refined molecular taxonomy and spatial resolution may help advance precision oncology in PDAC through informative stratification in clinical trials and insights into compartment-specific therapies.

Citation Format: William L. Hwang, Karthik A. Jagadeesh, Jimmy A. Guo, Hannah I. Hoffman, Payman Yadollahpour, Jason Reeves, Eugene Drokhlyansky, Nicholas Van Wittenberghe, Samouil Farhi, Denis Schapiro, George Eng, Jason M. Schenkel, William A. Freed-Pastor, Orr Ashenberg, Clifton Rodrigues, Domenic Abbondanza, Toni Delorey, Devan Phillips, Jorge Roldan, Debora Ciprani, Marina Kern, Jaimie L. Barth, Daniel R. Zollinger, Kit Fuhrman, Robin Fropf, Joseph Beechem, Colin Weekes, Cristina R. Ferrone, Jennifer Y. Wo, Theodore S. Hong, Orit Rozenblatt-Rosen, Andrew J. Aguirre, Mari Mino-Kenudson, Carlos Fernandez-del- Castillo, Andrew S. Liss, David T. Ting, Tyler Jacks, Aviv Regev. Multi-compartment reprogramming and spatially-resolved interactions in frozen pancreatic cancer with and without neoadjuvant chemotherapy and radiotherapy at single-cell resolution [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 94.

Extracellular Vesicle Analysis Allows for Identification of Invasive IPMN

BACKGROUND AND AIMS

Advances in cross-sectional imaging have resulted in increased detection of intraductal papillary mucinous neoplasms (IPMNs), and their management remains controversial. At present, there is no reliable noninvasive method to distinguish between indolent and high risk IPMNs. We performed extracellular vesicle (EV) analysis to identify markers of malignancy in an attempt to better stratify these lesions.

METHODS

Using a novel ultrasensitive digital extracellular vesicle screening technique (DEST), we measured putative biomarkers of malignancy (MUC1, MUC2, MUC4, MUC5AC, MUC6, Das-1, STMN1, TSP1, TSP2, EGFR, EpCAM, GPC1, WNT-2, EphA2, S100A4, PSCA, MUC13, ZEB1, PLEC1, HOOK1, PTPN6, and FBN1) in EV from patient-derived cell lines and then on circulating EV obtained from peripheral blood drawn from patients with IPMNs. We enrolled a total of 133 patients in two separate cohorts: a clinical discovery cohort (n = 86) and a validation cohort (n = 47).

RESULTS

From 16 validated EV proteins in plasma samples collected from the discovery cohort, only MUC5AC showed significantly higher levels in high-grade lesions. Of the 11 patients with invasive IPMN (inv/HG), 9 had high MUC5AC expression in plasma EV of the 11 patients with high-grade dysplasia alone, only 1 had high MUC5AC expression (sensitivity of 82%, specificity of 100%). These findings were corroborated in a separate validation cohort. The addition of MUC5AC as a biomarker to imaging and high-riskstigmata allowed detection of all cases requiring surgery, whereas imaging and high-risk stigmata alone would have missed 5 of 14 cases (36%).

CONCLUSIONS

MUC5AC in circulating EV can predict the presence of invasive carcinoma within IPMN. This approach has the potential to improve the management and follow-up of patients with IPMN including avoiding unnecessary surgery.

Transcriptomic Analysis of Laser Capture Microdissected Tumors Reveals Cancer- and Stromal-Specific Molecular Subtypes of Pancreatic Ductal Adenocarcinoma

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) lethality is multifactorial; although studies have identified transcriptional and genetic subsets of tumors with different prognostic significance, there is limited understanding of features associated with the minority of patients who have durable remission after surgical resection. In this study, we performed laser capture microdissection (LCM) of PDAC samples to define their cancer- and stroma-specific molecular subtypes and identify a prognostic gene expression signature for short-term and long-term survival.

EXPERIMENTAL DESIGN

LCM and RNA sequencing (RNA-seq) analysis of cancer and adjacent stroma of 19 treatment-naïve PDAC tumors was performed. Gene expression signatures were tested for their robustness in a large independent validation set. An RNA-ISH assay with pooled probes for genes associated with disease-free survival (DFS) was developed to probe 111 PDAC tumor samples.

RESULTS

Gene expression profiling identified four subtypes of cancer cells (C1-C4) and three subtypes of cancer-adjacent stroma (S1-S3). These stroma-specific subtypes were associated with DFS (P = 5.55E-07), with S1 associated with better prognoses when paired with C1 and C2. Thirteen genes were found to be predominantly expressed in cancer cells and corresponded with DFS in a validation using existing RNA-seq datasets. A second validation on an independent cohort of patients using RNA-ISH probes to six of these prognostic genes demonstrated significant association with overall survival (median 17 vs. 25 months; P < 0.02).

CONCLUSIONS

Our results identified specific signatures from the epithelial and the stroma components of PDAC, which add clarity to the nature of PDAC molecular subtypes and may help predict survival.

Simultaneous targeting of primary tumor, draining lymph node, and distant metastases through high endothelial venule-targeted delivery

Cancer patients with malignant involvement of tumor-draining lymph nodes (TDLNs) and distant metastases have the poorest prognosis. A drug delivery platform that targets the primary tumor, TDLNs, and metastatic niches simultaneously, remains to be developed. Here, we generated a novel monoclonal antibody (MHA112) against peripheral node addressin (PNAd), a family of glycoproteins expressed on high endothelial venules (HEVs), which are present constitutively in the lymph nodes (LNs) and formed ectopically in the tumor stroma. MHA112 was endocytosed by PNAd-expressing cells, where it passed through the lysosomes. MHA112 conjugated antineoplastic drug Paclitaxel (Taxol) (MHA112-Taxol) delivered Taxol effectively to the HEV-containing tumors, TDLNs, and metastatic lesions. MHA112-Taxol treatment significantly reduced primary tumor size as well as metastatic lesions in a number of mouse and human tumor xenografts tested. These data, for the first time, indicate that human metastatic lesions contain HEVs and provide a platform that permits simultaneous targeted delivery of antineoplastic drugs to the three key sites of primary tumor, TDLNs, and metastases.

Case Report: A Rare Case of Esophagogastric Junctional Squamous Cell Carcinoma After the Successful Treatment of Neuroendocrine Carcinoma: Clonal Tumor Evolution Revealed by Genetic Analysis

Neuroendocrine carcinoma (NEC) of the esophagogastric junction (EGJ) is a rare disease with no established treatments. Herein, we describe a case of recurrent squamous cell carcinoma (SCC) after achieving complete response to chemotherapy against NEC of the EGJ. A 67-year-old man was referred to our hospital because of epigastric discomfort. Computed tomography imaging and esophagogastroduodenoscopy revealed ulcerated tumors at the EGJ. Endoscopic biopsy revealed small tumor cells with a high nuclear/cytoplasmic ratio, suggesting small-cell NEC. Immunohistochemistry (IHC) analysis showed tumor cells with an MIB-1 index of 80%. The patient achieved complete response after 10 cycles of chemotherapy. Follow-up endoscopic examination revealed small red-colored mucosal lesions in the center of the cicatrized primary lesion. Re-biopsy detected cancer cells harboring large eosinophilic cytoplasm with keratinization and no evidence of NEC components. IHC of the cells were cytokeratin 5/6-positive and p53-negative. The tumor persisted without evidence of metastases after chemoradiotherapy, and total gastrectomy with lymph node dissection was performed. Pathological assessment of the resected specimens revealed SCC, without evidence of NEC. The patient survived without a recurrence for >3 years after the initial presentation. Somatic mutation profiles of the primary NEC and recurrent SCC were analyzed by targeted amplicon sequencing covering common cancer-related mutations. Both tumors possessed TP53 Q192X mutation, whereas SMAD4 S517T was found only in SCC, suggesting that both tumor components originated from a founder clone with a stop-gain mutation in TP53. The somatic mutation profile of the tumors indicated that that loss of heterozygosity (LOH) at the TP53 gene might have occurred during the differentiation of the founder clone into NEC, while a SMAD4 mutation might have contributed to SCC development, indicating branching and subclonal evolution from common founder clone to both NEC and SCC. The mutation assessments provided valuable information to better understand the clonal evolution of metachronous cancers.

Abstract PR-007: Single-nucleus and spatial transcriptomics of archival pancreatic ductal adenocarcinoma reveals multi-compartment reprogramming after neoadjuvant treatment

Molecular subtyping of pancreatic ductal adenocarcinoma (PDAC) remains in its nascent stages and does not currently inform clinical management or therapeutic development. Previously identified bulk expression subtypes in the untreated setting were influenced by contaminating stroma whereas single cell RNA-seq (scRNA-seq) of fresh tumors under-represented key cell types. Two consensus subtypes have arisen from these prior efforts: (1) classical-pancreatic, encompassing a spectrum of pancreatic lineage precursors, and (2) basal-like/squamous/quasi-mesenchymal, characterized by loss of endodermal identity and aberrations in chromatin modifiers. Basal-like tumors were associated with poorer responses to chemotherapy and worse survival in the metastatic setting but attempts to refine this binary classification have failed to further stratify patient survival. Recent clinical trials have supported the increasing adoption of neoadjuvant therapy to aggressively address the risk of micro-metastatic spread and to circumvent concerns of treatment tolerance in the postoperative setting. There is an urgent need to understand how preoperative treatment reprograms residual tumor cells to identify additional therapeutic vulnerabilities that can be exploited in combination with neoadjuvant CRT. Here, we developed a robust single-nucleus RNA-seq (snRNA-seq) technique for frozen archival PDAC specimens and used it to study both untreated tumors (n = 15) and those that received neoadjuvant CRT (n = 11). Gene expression programs learned across malignant cell and fibroblast profiles uncovered a clinically relevant molecular taxonomy with improved prognostic stratification (median survival: 11.2 months in highest risk group to 44.7 months in lowest risk group) compared to prior classifications. Moreover, in the neoadjuvant treatment context, there was lower expression of classical-like phenotypes in malignant cells in favor of basal-like phenotypes associated with TNF-NFkB and interferon signaling as well as the presence of novel acinar and neuroendocrine classical-like states, which may be more resilient to cytotoxic treatment. These results suggest that differentiated endodermal phenotypes are only prevalent enough to be detected under treatment selection pressure and when observed in treatment-naïve bulk studies, may reflect normal cell contamination. Spatially-resolved transcriptomics revealed an association between malignant cells expressing basal-like programs and higher immune infiltration with increased lymphocytic content, whereas those exhibiting classical-like programs were linked to sparser macrophage-predominant microniches, perhaps pointing to distinct therapeutic susceptibilities. Our refined molecular taxonomy and spatial resolution may help advance precision oncology in PDAC through informative stratification in clinical trials and insights into differential therapeutic targeting leveraging the immune system.

Citation Format: William L. Hwang, Karthik A. Jagadeesh, Jimmy A. Guo, Hannah I. Hoffman, Eugene Drokhlyansky, Nicholas Van Wittenberghe, Samouil Farhi, Denis Schapiro, Jason Reeves, Daniel R. Zollinger, George Eng, Jason M. Schenkel, William A. Freed-Pastor, Clifton Rodrigues, Domenic Abbondanza, Debora Ciprani, Jennifer Y. Wo, Theodore S. Hong, Andrew J. Aguirre, Orit Rozenblatt-Rosen, Mari Mino-Kenudson, Carlos Fernandez-del Castillo, Andrew S. Liss, Tyler E. Jacks, Aviv Regev. Single-nucleus and spatial transcriptomics of archival pancreatic ductal adenocarcinoma reveals multi-compartment reprogramming after neoadjuvant treatment [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PR-007.

Neoplastic-Stromal Cell Cross-talk Regulates Matrisome Expression in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a highly desmoplastic reaction, warranting intense cancer-stroma communication. In this study, we interrogated the contribution of the BET family of chromatin adaptors to the cross-talk between PDAC cells and the tumor stroma. Short-term treatment of orthotopic xenograft tumors with CPI203, a small-molecule inhibitor of BET proteins, resulted in broad changes in the expression of genes encoding components of the extracellular matrix (matrisome) in both cancer and stromal cells. Remarkably, more than half of matrisome genes were expressed by cancer cells. In vitro cocultures of PDAC cells and cancer-associated fibroblasts (CAF) demonstrated that matrisome expression was regulated by BET-dependent cancer-CAF cross-talk. Disrupting this cross-talk in vivo resulted in diminished growth of orthotopic patient-derived xenograft tumors, reduced proliferation of cancer cells, and changes in collagen structure consistent with that of patients who experienced better survival. Examination of matrisome gene expression in publicly available data sets of 573 PDAC tumors identified a 65-gene signature that was able to distinguish long- and short-term PDAC survivors. Importantly, the expression of genes predictive of short-term survival was diminished in the cancer cells of orthotopic xenograft tumors of mice treated with CPI203. Taken together, these results demonstrate that inhibiting the activity BET proteins results in transcriptional and structural differences in the matrisome are associated with better patient survival. IMPLICATIONS: These studies highlight the biological relevance of the matrisome program in PDAC and suggest targeting of epigenetically driven tumor-stroma cross-talk as a potential therapeutic avenue.

Pancreatic circulating tumor cell profiling identifies LIN28B as a metastasis driver and drug target

Pancreatic ductal adenocarcinoma (PDAC) lethality is due to metastatic dissemination. Characterization of rare, heterogeneous circulating tumor cells (CTCs) can provide insight into metastasis and guide development of novel therapies. Using the CTC-iChip to purify CTCs from PDAC patients for RNA-seq characterization, we identify three major correlated gene sets, with stemness genes LIN28B/KLF4, WNT5A, and LGALS3 enriched in each correlated gene set; only LIN28B CTC expression was prognostic. CRISPR knockout of LIN28B-an oncofetal RNA-binding protein exerting diverse effects via negative regulation of let-7 miRNAs and other RNA targets-in cell and animal models confers a less aggressive/metastatic phenotype. This correlates with de-repression of let-7 miRNAs and is mimicked by silencing of downstream let-7 target HMGA2 or chemical inhibition of LIN28B/let-7 binding. Molecular characterization of CTCs provides a unique opportunity to correlated gene set metastatic profiles, identify drivers of dissemination, and develop therapies targeting the "seeds" of metastasis.

FOLFIRINOX Versus Gemcitabine-based Therapy for Pancreatic Ductal Adenocarcinoma: Lessons from Patient-derived Cell Lines

BACKGROUND/AIM

FOLFIRINOX [fluorouracil (5-FU), irinotecan, oxaliplatin] and gemcitabine plus nab-paclitaxel are standard treatments for patients with pancreatic ductal adenocarcinoma (PDAC). Despite efficacy rates of less than 32%, evidence is lacking to guide the use of one drug over the other. Herein, we compared the sensitivity of patient-derived PDAC cell lines to each of these regimens.

MATERIALS AND METHODS

Changes in the growth of 19 low-passage patient-derived PDAC cell lines were evaluated in response to treatment with FOLFIRINOX and gemcitabine plus paclitaxel (Gem-Pac).

RESULTS

Six cell lines exhibited optimal sensitivity (high EMax and low GI50) to FOLFIRINOX and three cell lines exhibited optimal sensitivity to Gem-Pac. Several cell lines that were optimally sensitive to one drug regimen exhibited very poor response to the other.

CONCLUSION

Further characterization of cancer cells exhibiting preferential sensitivity to each of these regimens may allow the identification of biomarkers to guide the selection of appropriate chemotherapy for a given patient.

A fast, simple, and cost-effective method of expanding patient-derived xenograft mouse models of pancreatic ductal adenocarcinoma

BACKGROUND

Patient-derived xenograft (PDX) mouse models of cancer have been recognized as better mouse models that recapitulate the characteristics of original malignancies including preserved tumor heterogeneity, lineage hierarchy, and tumor microenvironment. However, common challenges of PDX models are the significant time required for tumor expansion, reduced tumor take rates, and higher costs. Here, we describe a fast, simple, and cost-effective method of expanding PDX of pancreatic ductal adenocarcinoma (PDAC) in mice.

METHODS

We used two established frozen PDAC PDX tissues (derived from two different patients) and implanted them subcutaneously into SCID mice. After tissues reached 10-20 mm in diameter, we performed survival surgery on each mouse to harvest 90-95% of subcutaneous PDX (incomplete resection), allowing the remaining 5-10% of PDX to continue growing in the same mouse.

RESULTS

We expanded three consecutive passages (P1, P2, and P3) of PDX in the same mouse. Comparing the times required for in vivo expansion, P2 and P3 (expanded through incomplete resection) grew 26-60% faster than P1. Moreover, such expanded PDX tissues were successfully implanted orthotopically into mouse pancreases. Within 20 weeks using only 14 mice, we generated sufficient PDX tissue for future implantation of 200 mice. Our histology study confirmed that the morphologies of cancer cells and stromal structures were similar across all three passages of subcutaneous PDX and the orthotopic PDX and were reflective of the original patient tumors.

CONCLUSIONS

Taking advantage of incomplete resection of tumors associated with high local recurrence, we established a fast method of PDAC PDX expansion in mice.

Hedgehog signaling promotes angiogenesis directly and indirectly in pancreatic cancer

INTRODUCTION

The inhibition of Hedgehog (Hh) signaling in pancreatic ductal adenocarcinoma (PDAC) reduces desmoplasia and promotes increased vascularity. In contrast to these findings, the Hh ligand Sonic Hedgehog (SHH) is a potent proangiogenic factor in non-tumor models. The aim of this study was to determine the molecular mechanisms by which SHH affects the tumor stroma and angiogenesis.

METHODS

Mice bearing three different xenografted human PDAC (n = 5/group) were treated with neutralizing antibodies to SHH. After treatment for 7 days, tumors were evaluated and the expression of 38 pro- and antiangiogenic factors was assessed in the tumor cells and their stroma. The effect of SHH on the regulation of pro- and antiangiogenic factors in fibroblasts and its impact on endothelial cells was then further assessed in in vitro model systems.

RESULTS

Inhibition of SHH affected tumor growth, stromal content, and vascularity. Its effect on the Hh signaling pathway was restricted to the stromal compartment of the three cancers. SHH-stimulated angiogenesis indirectly through the reduction of antiangiogenic THBS2 and TIMP2 in stromal cells. An additional direct effect of SHH on endothelial cells depended on the presence of VEGF.

CONCLUSION

Inhibition of Hh signaling reduces tumor vascularity, suggesting that Hh plays a role in the maintenance or formation of the tumor vasculature. Whether the reduction in tumor growth and viability seen in the epithelium is a direct consequence of Hh pathway inhibition, or indirectly caused by its effect on the stroma and vasculature, remains to be evaluated.

Abstract A22: Molecular subtypes and resistance programs in pancreatic ductal adenocarcinoma elucidated with single-nucleus RNA-seq

Objective: Pancreatic ductal adenocarcinoma (PDAC) remains a treatment-refractory disease as existing molecular subtypes are insufficient and do not currently inform clinical decisions. Rare cell types, including those responsible for resistance, are difficult to detect with bulk transcriptomic profiling. Indeed, several previously identified transcriptomic subtypes of PDAC are unintentionally driven by “contaminating” stromal components. Single-cell transcriptomics provides an unprecedented degree of resolution into the properties of individual cells. However, RNA extraction from RNase- and stroma-rich pancreatic tissue is difficult and prior single-cell efforts have been limited by suboptimal dissociation/RNA quality. We developed a robust single-nucleus RNA-seq (sNuc-seq) technique compatible with frozen archival PDAC specimens and computational techniques to identify the transcriptomic programs driving tumor subtypes and therapeutic resistance.

Methods: Patients with localized PDAC undergoing surgical resection with or without neoadjuvant chemoradiotherapy were consented for this IRB-approved study. Specimens were screened for RNA Integrity Number &gt;6. Single nuclei suspensions were extracted from flash-frozen primary PDAC specimens and organoids. Approximately 8,000 nuclei were loaded on the 10x Genomics Chromium platform per sample to generate and sequence 3’ gene expression libraries (Illumina HiSeq 2500, 125 bp paired-end reads). sNuc-seq derived reads were processed using the 10X CellRanger v3.0.2 pipeline. Unsupervised clustering was utilized to identify different cell populations and known marker genes from literature were used to label cell types.

Results: Both treatment-naïve (n=12) and treatment-resistant (n=11) specimens yielded high-quality sNuc-seq data (&gt;1,000 nuclei per sample, &gt;1,000 median genes per nucleus). In each tumor, distinct clusters with gene expression profiles consistent with ductal, fibroblast, endothelial, endocrine, lymphocyte, and myeloid cell populations were identified. Malignant cells were confirmed by inferred copy number variation analysis (InferCNV v3.9) and segregated into several distinct clusters for each individual patient highlighting intratumoral heterogeneity. While some malignant clusters corresponded to previously identified basal-squamous and classical-progenitor bulk subtypes, others featured expression profiles distinct from known subtypes, including cells with upregulation of hypoxia-associated or cytoskeletal genes.

Conclusions: Applying sNuc-seq to treatment-naïve and pretreated PDAC specimens, we uncovered significant intratumoral heterogeneity in the malignant and stromal compartments and identified malignant cells featuring transcriptomic programs that do not fit previously identified bulk subtypes. Characterization of therapeutic resistance programs, spatial relationships among cell types, and association with clinical outcomes is ongoing.

Citation Format: William L. Hwang, Karthik A. Jagadeesh, Orr Ashenberg, Eugene Drokhlyansky, George Eng, Nicholas Van Wittenberghe, William Freed-Pastor, Clifton Rodriguez, Danielle Dionne, Julia Waldman, Michael Cuoco, Alexander Tsankov, Connor Lambden, Caroline Porter, Jason Schenkel, Laurens Lambert, Debora Ciprani, Andrew J. Aguirre, Mari Mino-Kenudson, Theodore S. Hong, Orit Rozenblatt-Rosen, Carlos Fernandez-del Castillo, Andrew S. Liss, Aviv Regev, Tyler E. Jacks. Molecular subtypes and resistance programs in pancreatic ductal adenocarcinoma elucidated with single-nucleus RNA-seq [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A22.

Abstract B06: The angiotensin receptor blocker and partial PPARγ agonist telmisartan inhibits the growth of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is highly resistant to chemotherapy, partly due to the presence of a dense-fibrotic stroma and adaptive metabolism. Telmisartan is an angiotensin II type receptor 1 (AT1) antagonist with partial peroxisome proliferator-activated receptor gamma (PPARγ) agonistic activity used for treatment of hypertension. The aim of this study was to determine the effects of telmisartan on the viability of PDAC cells and tumor progression. In panels of 4 murine and 8 human PDAC cells, the telmisartan IC50 was lower in cells with a low steady-state expression of PPARγ and a mesenchymal cell morphology. In contrast, losartan—a selective AT1 inhibitor—did not affect the viability of PDAC cells. The siRNA knockdown of PPARγ enhanced the sensitivity of telmisartan and stimulated epithelial-mesenchymal transition, which was accompanied by an increase in Wnt signaling. PPARγ regulates glucose metabolism and autophagy. We thus assessed effects of telmisartan on bioenergetics and autophagy of PDAC cells. In PPARγ-knockdown and -scrambled cells telmisartan significantly reduced glucose uptake, without affecting ATP production, but increased respiratory capacity, which can maintain the production of ATP during hypoglycemia. Immunoblotting revealed that PPARγ knockdown compared to scramble cells had increased levels of phosphorylated-AMP-activated protein kinase (p-AMPK) and increased expression of LC3A/B—structural proteins of autophagosomal membranes—which implies higher levels of autophagy. We also compared effects of telmisartan treatment on LC3A/B expression to well-established autophagy modulators, chloroquine and verapamil. Under nutrient-rich conditions and as expected, chloroquine and verapamil treatment induced LC3A/B accumulation, consistent with active autophagic flux in these cells. Telmisartan treatment decreased the levels of LC3A/B in both scramble and PPARγ knockdown cells and decreased the formation of LC3A/B positive granules in other PDAC cell lines. Telmisartan can also induce the accumulation of the signal adaptor protein p62 (SQSTM1), even in the presence of verapamil, which is also consistent with autophagy inhibition. Telmisartan did not prevent the accumulation LC3A/B in the presence of chloroquine, implying that telmisartan acts after the autophagosome-lysosome fusion step. To assess the effects of telmisartan in vivo, we used an orthotopic PDAC model. Telmisartan monotherapy inhibited the growth of primary tumors, decreased the incidence of liver metastasis, and significantly improved the survival of mice. Hence, telmisartan can reduce autophagy and the viability of PDAC cells, and PDAC progression. Because telmisartan is an FDA-approved drug, our findings provide the scientific rationale for testing its efficacy in the prevention of PDAC progression.

Citation Format: Jelena Grahovac, Shiwei Han, Hao Liu, Mark Duquette, Alba Luengo, Daniel Schanne, Andrew S. Liss, Matthew G. Vander Heiden, Rakesh K. Jain, Yves Boucher. The angiotensin receptor blocker and partial PPARγ agonist telmisartan inhibits the growth of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr B06.

Stromal Microenvironment Shapes the Intratumoral Architecture of Pancreatic Cancer

Single-cell technologies have described heterogeneity across tissues, but the spatial distribution and forces that drive single-cell phenotypes have not been well defined. Combining single-cell RNA and protein analytics in studying the role of stromal cancer-associated fibroblasts (CAFs) in modulating heterogeneity in pancreatic cancer (pancreatic ductal adenocarcinoma [PDAC]) model systems, we have identified significant single-cell population shifts toward invasive epithelial-to-mesenchymal transition (EMT) and proliferative (PRO) phenotypes linked with mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) signaling. Using high-content digital imaging of RNA in situ hybridization in 195 PDAC tumors, we quantified these EMT and PRO subpopulations in 319,626 individual cancer cells that can be classified within the context of distinct tumor gland "units." Tumor gland typing provided an additional layer of intratumoral heterogeneity that was associated with differences in stromal abundance and clinical outcomes. This demonstrates the impact of the stroma in shaping tumor architecture by altering inherent patterns of tumor glands in human PDAC.

Lubricin/proteoglycan 4 detected in vocal folds of humans and five other mammals

OBJECTIVES/HYPOTHESIS

Lubricin/proteoglycan-4 (PRG4) lubricates connective tissues such as joints and tendon sheaths, enabling them to better withstand shearing and frictional forces during motion. We wondered whether PRG4 might play a role in phonation, as normal vocal folds withstand repetitive, high-velocity deformations remarkably well. As a first step, we tested whether PRG4 is expressed in vocal folds.

STUDY DESIGN

Laboratory study.

METHODS

Anatomical and molecular methods were applied to 47 larynges from humans, macaque (Macaca fascicularis), canines, pigs, calves, and rats. Immunohistochemistry (IHC), Western blot, and quantitative real-time polymerase chain reaction (qRT-PCR) methods were used to test for the presence of PRG4.

RESULTS

In all species, the true vocal fold lamina propria (TVF-LP) was positive for PRG4 by IHC, whereas immunoreactivity of the false vocal fold was weak or absent, depending on the species. Human TVF-LP was strongly stained across all layers. Immunoreactivity was seen variably on the vocal fold surface and within the vocal fold epithelium, in the conus elasticus and thyroglottic ligament, and at the tip of vocal process. Western blots of four humans and six pigs demonstrated immunoreactivity at appropriate molecular weight. qRT-PCR of pig tissues confirmed PRG4 mRNA expression, which was highest in the TVF-LP.

CONCLUSIONS

PRG4 was found in phonatory tissues of six mammals. We suggest it might act as a lubricant within the lamina propria and possibly on the vocal fold surface, limiting phonation-related damage to vocal fold extracellular matrix and epithelium, and enhancing vocal efficiency by reducing internal friction (viscosity) within the vocal fold.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E229-E237, 2019.

Mutant GNAS drives pancreatic tumourigenesis by inducing PKA-mediated SIK suppression and reprogramming lipid metabolism

G protein αs (GNAS) mediates receptor-stimulated cAMP signalling, which integrates diverse environmental cues with intracellular responses. GNAS is mutationally activated in multiple tumour types, although its oncogenic mechanisms remain elusive. We explored this question in pancreatic tumourigenesis where concurrent GNAS and KRAS mutations characterize pancreatic ductal adenocarcinomas (PDAs) arising from intraductal papillary mucinous neoplasms (IPMNs). By developing genetically engineered mouse models, we show that GnasR201C cooperates with KrasG12D to promote initiation of IPMN, which progress to invasive PDA following Tp53 loss. Mutant Gnas remains critical for tumour maintenance in vivo. This is driven by protein-kinase-A-mediated suppression of salt-inducible kinases (Sik1-3), associated with induction of lipid remodelling and fatty acid oxidation. Comparison of Kras-mutant pancreatic cancer cells with and without Gnas mutations reveals striking differences in the functions of this network. Thus, we uncover Gnas-driven oncogenic mechanisms, identify Siks as potent tumour suppressors, and demonstrate unanticipated metabolic heterogeneity among Kras-mutant pancreatic neoplasms.

Tumor engraftment in patient-derived xenografts of pancreatic ductal adenocarcinoma is associated with adverse clinicopathological features and poor survival

Patient-derived xenograft (PDX) tumors are powerful tools to study cancer biology. However, the ability of PDX tumors to model the biological and histological diversity of pancreatic ductal adenocarcinoma (PDAC) is not well known. In this study, we subcutaneously implanted 133 primary and metastatic PDAC tumors into immunodeficient mice. Fifty-seven tumors were successfully engrafted and even after extensive passaging, the histology of poorly-, moderately-, and well-differentiated tumors was maintained in the PDX models. Moreover, the fibroblast and collagen contents in the stroma of patient tumors were recapitulated in the corresponding PDX models. Analysis of the clinicopathological features of patients revealed xenograft tumor engraftment was associated with lymphovascular invasion (P = 0.001) and worse recurrence-free (median, 7 vs. 16 months, log-rank P = 0.047) and overall survival (median, 13 vs. 21 months, log-rank P = 0.038). Among successful engraftments, median time of growth required for reimplantation into new mice was 151 days. Reflective of the inherent biological diversity between PDX tumors with rapid (<151 days) and slow growth, differences in their growth were maintained during extensive passaging. Rapid growth was additionally associated with lymph node metastasis (P = 0.022). The association of lymphovascular invasion and lymph node metastasis with PDX formation and rapid growth may reflect an underlying biological mechanism that allows these tumors to adapt and grow in a new environment. While the ability of PDX tumors to mimic the cellular and non-cellular features of the parental tumor stroma provides a valuable model to study the interaction of PDAC cells with the tumor microenvironment, the association of successful engraftment with adverse clinicopathological features suggests PDX models over represent more aggressive forms of this disease.

Cytologic characteristics of circulating epithelioid cells in pancreatic disease

BACKGROUND

Circulating epithelioid cells (CECs), also known as circulating tumor, circulating cancer, circulating epithelial, or circulating nonhematologic cells, are a prognostic factor in various malignancies that can be isolated via various protocols. In the current study, the authors analyzed the cytomorphologic characteristics of CECs isolated by size in a cohort of patients with benign and malignant pancreatic diseases to determine whether cytomorphological features could predict CEC origin.

METHODS

Blood samples were collected from 9 healthy controls and 171 patients with pancreatic disease who were presenting for surgical evaluation before treatment. Blood was processed with the ScreenCell size-based filtration device. Evaluable CECs were analyzed in a blinded fashion for cytomorphologic characteristics, including cellularity; nucleoli; nuclear size, irregularity, variability, and hyperchromasia; and nuclear-to-cytoplasmic ratio. Statistical differences between variables were analyzed via the Fisher exact test.

RESULTS

No CECs were identified among the 9 normal healthy controls. Of the 115 patients with CECs (positive or suspicious for), 25 had nonmalignant disease and 90 had malignancy. There were no significant differences in any of the cytologic criteria noted between groups divided by benign versus malignant, neoplastic versus nonneoplastic, or pancreatic ductal adenocarcinoma versus neuroendocrine tumor.

CONCLUSIONS

CECs were observed in patients with malignant and nonmalignant pancreatic disease, but not in healthy controls. There were no morphologic differences observed between cells from different pancreatic diseases, suggesting that numerous conditions may be associated with CECs in the circulation and that care must be taken not to overinterpret cells identified by cytomorphology as indicative of circulating tumor cells of pancreatic cancer. Additional studies are required to determine the origin and clinical significance of these cells. Cancer Cytopathol 2017;125:332-340. © 2017 American Cancer Society.

Loss of Trefoil Factor 2 From Pancreatic Duct Glands Promotes Formation of Intraductal Papillary Mucinous Neoplasms in Mice

BACKGROUND & AIMS

Little is known about the origin of pancreatic intraductal papillary mucinous neoplasms (IPMN). Pancreatic duct glands (PDGs) are gland-like outpouches budding off the main pancreatic ducts that function as a progenitor niche for the ductal epithelium; they express gastric mucins and have characteristics of side-branch IPMNs. We investigated whether PDGs are a precursor compartment for IPMNs and the role of Trefoil factor family 2 (TFF2)-a protein expressed by PDGs and the gastric mucosa that are involved in epithelial repair and tumor suppression.

METHODS

We obtained pancreatectomy specimens from 20 patients with chronic pancreatitis, 13 with low-grade side-branch IPMNs, and 15 patients with PDAC; histologically normal pancreata were used as controls (n = 18). Samples were analyzed by immunohistochemistry to detect TFF1 and TFF2 and cell proliferation. We performed mitochondrial DNA mutational mapping studies to determine the cell lineage and fate of PDG cells. Pdx1-Cre;LSL-KRAS^G12D (KC) mice were bred with TFF2-knockout mice to generate KC/Tff2^-/- and KC/Tff2^+/- mice. Pancreata were collected and histologically analyzed for formation of IPMN, pancreatic intraepithelial neoplasias, and PDAC, in addition to proliferation and protein expression. Human pancreatic ductal epithelial cells and PDAC cell lines were transfected with vectors to overexpress or knock down TFF2 or SMAD4.

RESULTS

Histologic analysis of human samples revealed gastric-type IPMN to comprise 2 molecularly distinct layers: a basal crypt segment that expressed TFF2 and overlying papillary projections. Proliferation occurred predominantly in the PDG-containing basal segments. Mitochondrial mutation mapping revealed a 97% match between the profiles of proliferating PDG cells and their overlying nonproliferative IPMN cells. In contrast to KC mice, 2-month-old KC/Tff2^+/- and KC/Tff2^-/- mice developed prominent papillary structures in the duct epithelium with cystic metaplasia of the PDG, which resembled human IPMN; these expressed gastric mucins (MUC5AC and MUC6), but not the intestinal mucin MUC2. KC/TFF2-knockout mice developed a greater number and higher grade of pancreatic intraepithelial neoplasias than KC mice, and 1 mouse developed an invasive adenocarcinoma. Expression of TFF2 reduced proliferation of PDAC cells 3-fold; this effect required up-regulation and activation of SMAD4. We found expression of TFF2 to be down-regulated in human PDAC by hypermethylation of its promoter.

CONCLUSIONS

In histologic analyses of human IPMNs, we found PDGs to form the basal segment and possibly serve as a progenitor compartment. TFF2 has tumor-suppressor activity in the mouse pancreas and prevents formation of mucinous neoplasms.

A Size-Selective Intracellular Delivery Platform

Identifying and separating a subpopulation of cells from a heterogeneous mixture are essential elements of biological research. Current approaches require detailed knowledge of unique cell surface properties of the target cell population. A method is described that exploits size differences of cells to facilitate selective intracellular delivery using a high throughput microfluidic device. Cells traversing a constriction within this device undergo a transient disruption of the cell membrane that allows for cytoplasmic delivery of cargo. Unique constriction widths allow for optimization of delivery to cells of different sizes. For example, a 4 μm wide constriction is effective for delivery of cargo to primary human T-cells that have an average diameter of 6.7 μm. In contrast, a 6 or 7 μm wide constriction is best for large pancreatic cancer cell lines BxPc3 (10.8 μm) and PANC-1 (12.3 μm). These small differences in cell diameter are sufficient to allow for selective delivery of cargo to pancreatic cancer cells within a heterogeneous mixture containing T-cells. The application of this approach is demonstrated by selectively delivering dextran-conjugated fluorophores to circulating tumor cells in patient blood allowing for their subsequent isolation and genomic characterization.

Isocitrate Dehydrogenase Mutations Confer Dasatinib Hypersensitivity and SRC Dependence in Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is an aggressive liver bile duct malignancy exhibiting frequent isocitrate dehydrogenase (IDH1/IDH2) mutations. Through a high-throughput drug screen of a large panel of cancer cell lines, including 17 biliary tract cancers, we found that IDH mutant (IDHm) ICC cells demonstrate a striking response to the multikinase inhibitor dasatinib, with the highest sensitivity among 682 solid tumor cell lines. Using unbiased proteomics to capture the activated kinome and CRISPR/Cas9-based genome editing to introduce dasatinib-resistant "gatekeeper" mutant kinases, we identified SRC as a critical dasatinib target in IDHm ICC. Importantly, dasatinib-treated IDHm xenografts exhibited pronounced apoptosis and tumor regression. Our results show that IDHm ICC cells have a unique dependency on SRC and suggest that dasatinib may have therapeutic benefit against IDHm ICC. Moreover, these proteomic and genome-editing strategies provide a systematic and broadly applicable approach to define targets of kinase inhibitors underlying drug responsiveness.

SIGNIFICANCE

IDH mutations define a distinct subtype of ICC, a malignancy that is largely refractory to current therapies. Our work demonstrates that IDHm ICC cells are hypersensitive to dasatinib and critically dependent on SRC activity for survival and proliferation, pointing to new therapeutic strategies against these cancers. Cancer Discov; 6(7); 727-39. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 681.

Regulation of GLI Underlies a Role for BET Bromodomains in Pancreatic Cancer Growth and the Tumor Microenvironment

PURPOSE

The initiation, progression, and maintenance of pancreatic ductal adenocarcinoma (PDAC) results from the interplay of genetic and epigenetic events. While the genetic alterations of PDAC have been well characterized, epigenetic pathways regulating PDAC remain, for the most part, elusive. The goal of this study was to identify novel epigenetic regulators contributing to the biology of PDAC.

EXPERIMENTAL DESIGN

In vivo pooled shRNA screens targeting 118 epigenetic proteins were performed in two orthotopic PDAC xenograft models. Candidate genes were characterized in 19 human PDAC cell lines, heterotopic xenograft tumor models, and a genetically engineered mouse (GEM) model of PDAC. Gene expression, IHC, and immunoprecipitation experiments were performed to analyze the pathways by which candidate genes contribute to PDAC.

RESULTS

In vivo shRNA screens identified BRD2 and BRD3, members of the BET family of chromatin adaptors, as key regulators of PDAC tumor growth. Pharmacologic inhibition of BET bromodomains enhanced survival in a PDAC GEM model and inhibited growth of human-derived xenograft tumors. BET proteins contribute to PDAC cell growth through direct interaction with members of the GLI family of transcription factors and modulating their activity. Within cancer cells, BET bromodomain inhibition results in downregulation of SHH, a key mediator of the tumor microenvironment and canonical activator of GLI. Consistent with this, inhibition of BET bromodomains decreases cancer-associated fibroblast content of tumors in both GEM and xenograft tumor models.

CONCLUSIONS

Therapeutic inhibition of BET proteins offers a novel mechanism to target both the neoplastic and stromal components of PDAC. Clin Cancer Res; 22(16); 4259-70. ©2016 AACR.

A method for fixing and paraffin embedding tissue to retain the natural fluorescence of reporter proteins

Green fluorescent protein (GFP) and its derivatives are routinely employed as surrogate markers for gene expression and lineage tracing in genetically engineered mice. Tissues from these mice are commonly formalin fixed and paraffin embedded (FFPE) for histological studies. However, this results in inactivation of the natural fluorescence of these proteins, requiring their detection by immunological techniques. Here we present an ethanol fixation protocol that allows for the direct visualization of the natural fluorescence of reporter proteins while maintaining excellent tissue histology. We demonstrate the utility of this method for visualizing green and red fluorescent proteins in a wide range of murine tissues using both cytoplasmic and membrane-localized fluorescent reporter proteins. Tissues fixed by this method also allow for immunohistochemical studies, providing a single method to visualize the natural fluorescence of reporter proteins with subsequent detection of cellular proteins.

Circulating Epithelial Cells in Patients with Pancreatic Lesions: Clinical and Pathologic Findings

BACKGROUND

Circulating epithelial cell (CEC) isolation has provided diagnostic and prognostic information for a variety of cancers, previously supporting their identity as circulating tumor cells in the literature. However, we report CEC findings in patients with benign, premalignant, and malignant pancreatic lesions using a size-selective filtration device.

STUDY DESIGN

Peripheral blood samples were drawn from patients found to have pancreatic lesions on preoperative imaging at a surgical clinic. Blood was filtered using ScreenCell devices, which were evaluated microscopically by a pancreatic cytopathologist. Pathologic data and clinical outcomes of these patients were obtained from medical records during a 1-year follow-up period.

RESULTS

Nine healthy volunteers formed the control group and were found to be negative for CECs. There were 179 patients with pancreatic lesions that formed the study cohort. Circulating epithelial cells were morphologically similar in patients with a variety of pancreatic lesions. Specifically, CECs were identified in 51 of 105 pancreatic ductal adenocarcinomas (49%), 7 of 11 neuroendocrine tumors (64%), 13 of 21 intraductal papillary mucinous neoplasms (62%), and 6 of 13 patients with chronic pancreatitis. Rates of CEC identification were similar in patients with benign, premalignant, and malignant lesions (p = 0.41). In addition, CEC findings in pancreatic ductal adenocarcinoma patients were not associated with poor prognosis.

CONCLUSIONS

Although CECs were not identified in healthy volunteers, they were identified in patients with benign, premalignant, and malignant pancreatic lesions. The presence of CECs in patients presenting with pancreatic lesions is neither diagnostic of malignancy nor prognostic for patients with pancreatic ductal adenocarcinoma.

Pancreatic duct glands (PDGs) are a progenitor compartment responsible for pancreatic ductal epithelial repair

Pancreatic duct glands (PDGs) have molecular features known to mark stem cell niches, but their function remains to be determined. To investigate the role of PDGs as a progenitor niche, PDGs were analyzed in both humans and mice. Cells were characterized by immunohistochemistry and microarray analysis. In vivo proliferative activity and migration of PDG cells were evaluated using a BrdU tag-and-chase strategy in a mouse model of pancreatitis. In vitro migration assays were used to determine the role of trefoil factor (TFF) -1 and 2 in cell migration. Proliferative activity in the pancreatic epithelium in response to inflammatory injury is identified principally within the PDG compartment. These proliferating cells then migrate out of the PDG compartment to populate the pancreatic duct. Most of the pancreatic epithelial migration occurs within 5days and relies, in part, on TFF-1 and -2. After migration, PDG cells lose their PDG-specific markers and gain a more mature pancreatic ductal phenotype. Expression analysis of the PDG epithelium reveals enrichment of embryonic and stem cell pathways. These results suggest that PDGs are an epithelial progenitor compartment that gives rise to mature differentiated progeny that migrate to the pancreatic duct. Thus PDGs are a progenitor niche important for pancreatic epithelial regeneration.

Characterization of ATF2 in Rel/NFκB oncogenesis reveals its role in the regulation of Ras signaling

The v-Rel oncoprotein is the acutely transforming member of the Rel/NFκB family of transcription factors. v-Rel transforms cells through the inappropriate activation and suppression of genes normally regulated by cellular Rel/NFκB family members. We have recently demonstrated that activation of Ha-Ras by v-Rel contributes to transformation. Characterization of AP-1 family members in v-Rel-mediated transformation revealed ectopic expression of ATF2 inhibited transformation by blocking Ha-Ras activity. This lack of Ha-Ras activity prevented downstream activation of the Raf-MEK-ERK pathway, a critical pathway for v-Rel-mediated transformation. Microarray analysis of cells treated with an inhibitor to the ERK pathway revealed a relatively small number of genes that are specifically regulated by ERK activity in cells expressing v-Rel. These studies suggest the main contribution of ERK activity is to temper the expression of genes in v-Rel transformed cells. The mechanism by which ATF2 regulates Ras-Raf-MEK-ERK signaling appears to be a context dependent event. The ectopic expression of ATF2 in cells that are not expressing v-Rel results in the activation of Ha-Ras. However, activation of downstream Raf-MEK-ERK signaling pathway is blocked, likely through the recruitment of inhibitory 14-3-3 proteins to c-Raf. These results suggest a diverse role for ATF2 in the regulation of the Ras-Raf-MEK-ERK pathway.

Prognosis of invasive intraductal papillary mucinous neoplasm depends on histological and precursor epithelial subtypes

OBJECTIVE

Invasive cancers arising from intraductal papillary mucinous neoplasm (IPMN) are recognised as a morphologically and biologically heterogeneous group of neoplasms. Less is known about the epithelial subtypes of the precursor IPMN from which these lesions arise. The authors investigate the clinicopathological characteristics and the impact on survival of both the invasive component and its background IPMN.

DESIGN AND PATIENTS

The study cohort comprised 61 patients with invasive IPMN (study group) and 570 patients with pancreatic ductal adenocarcinoma (PDAC, control group) resected at a single institution. Multivariate analyses were performed using a stage-matched Cox proportional hazard model.

RESULTS

The histology of invasive components of the IPMN cohort was tubular in 38 (62%), colloid in 16 (26%), and oncocytic in seven (12%). Compared with PDAC, invasive IPMNs were associated with a lower incidence of adverse pathological features and improved mortality by multivariate analysis (HR 0.58; 95% CI 0.39 to 0.86). In subtype analysis, this favourable outcome remained only for colloid and oncocytic carcinomas, while tubular adenocarcinoma was associated with worse overall survival, not significantly different from that of PDAC (HR 0.85; 95% CI 0.53 to 1.36). Colloid and oncocytic carcinomas arose only from intestinal- and oncocytic-type IPMNs, respectively, and were mostly of the main-duct type, whereas tubular adenocarcinomas primarily originated in the gastric background, which was often associated with branch-duct IPMN. Overall survival of patients with invasive adenocarcinomas arising from gastric-type IPMN was significantly worse than that of patients with non-gastric-type IPMN (p=0.016).

CONCLUSIONS

Tubular, colloid and oncocytic invasive IPMNs have varying prognosis, and arise from different epithelial subtypes. Colloid and oncocytic types have markedly improved biology, whereas the tubular type has a course that resembles PDAC. Analysis of these subtypes indicates that the background epithelium plays an equally, if not more, important role in defining the biology and prognosis of invasive IPMNs.

ERK and JNK activation is essential for oncogenic transformation by v-Rel

v-Rel is the acutely oncogenic member of the NF-κB family of transcription factors. Infection with retroviruses expressing v-Rel rapidly induces fatal lymphomas in birds and transforms primary lymphocytes and fibroblasts in vitro. We have previously shown that AP-1 transcriptional activity contributes to v-Rel-mediated transformation. While v-Rel increases the expression of these factors, their activity may also be induced through phosphorylation by the mitogen-activated protein (MAP) kinases. The expression of v-Rel results in the strong and sustained activation of the ERK and JNK MAPK pathways. This induction is critical for the v-Rel transformed phenotype, as suppression of MAPK activity with chemical inhibitors or siRNA severely impairs colony formation of v-Rel transformed lymphoid cell lines. However, signaling must be maintained within an optimal range in these cells, since strong additional activation of either pathway beyond the levels induced by v-Rel through the expression of constitutively active MAPK proteins attenuates the transformed phenotype. MAPK signaling also plays an important role in the initial transformation of primary spleen cells by v-Rel, although distinct requirements for MAPK activity at different stages of v-Rel-mediated transformation were identified. We also show that the ability of v-Rel to induce MAPK signaling more strongly than c-Rel contributes to its greater oncogenicity.

Cell transformation by v-Rel reveals distinct roles of AP-1 family members in Rel/NF-kappaB oncogenesis

Cell transformation by the v-rel oncogene is mediated by the aberrant expression of genes that are normally tightly regulated by other Rel/NF-κB family members. Although a number of genes inappropriately activated or suppressed by v-Rel have been identified, their contributions to the v-Rel transformation process have been poorly characterized. Here, we examine the role of individual AP-1 proteins in v-Rel-mediated transformation. v-Rel transformed cells exhibit elevated RNA and protein expression of c-Fos, c-Jun, and ATF2 and sustained repression of Fra-2. c-Fos and c-Jun are essential in both the initiation and maintenance of v-Rel-mediated transformation while Fra-2 is dispensable. By employing a c-Jun dimerization mutant, we further identified Fos:Jun heterodimers as major contributors to the v-Rel transformation process. The inability of c-Rel to induce the expression of c-Fos and c-Jun contributes to its weaker oncogenic potential relative to v-Rel. Our studies also demonstrate that v-Rel may induce AP-1 members by directly upregulating gene expression (c-fos and ATF2) and by activating pathways that stimulate AP-1 activity. While elevated expression of ATF2 is also required for v-Rel-mediated transformation, its ectopic overexpression is inhibitory. Investigating the mode of ATF2 regulation revealed a positive feedback mechanism whereby ATF2 induces p38 MAPK phosphorylation to further induce its own activity. In addition, these studies identified Ha-Ras as an effector of v-Rel mediated transformation and reveal a novel role for ATF2 in the inhibition of the Ras-Raf-MEK-ERK signaling pathway. Overall, these studies reveal distinct and complex roles of AP-1 proteins in Rel/NF-κB oncogenesis.

Targeted disruption of Mib2 causes exencephaly with a variable penetrance

Mib1 and Mib2 ubiquitin ligases are very similar in their domain construction. They partake in the Notch signaling pathway by ubiquitinating the Notch receptors Delta and Jagged prior to endocytosis. We have created a targeted mutation of Mib2 and show that its phenotype is a variable penetrance, failure to close the cranial neural tube. The penetrance depends on the genetic background but it appears that Mib2 is not completely essential in mouse development.

Mechanism of telomerase activation by v-Rel and its contribution to transformation

Telomerase is activated during the transformation of lymphoid cells and fibroblasts by v-Rel, the oncogenic member of the Rel/NF-kappaB family of transcription factors. v-Rel-transformed cell lines have longer telomeres than untransformed chicken lymphoid cells and have high levels of telomerase activity. v-Rel-mediated activation of telomerase is achieved by multiple mechanisms. The expression of the gene encoding the catalytic subunit of telomerase (TERT) was directly upregulated by v-Rel. Moreover, the expression of v-Rel altered the ratio of alternatively spliced and full-length TERT transcripts in favor of the full-length forms. The activation of telomerase by v-Rel in lymphocytes was also accompanied by inactivation of nuclear inhibitors. The inhibition of telomerase activity in v-Rel-transformed cell lines led to apoptosis within 24 h. The expression of v-Rel in a macrophage cell line resulted in elevated levels of reactive oxygen species (ROS), increased telomerase activity, and increased sensitivity to telomerase inhibitors. In contrast, the ectopic expression of TERT decreased the extent of apoptosis induced by ROS. The activation of telomerase by v-Rel may, therefore, partially protect the transformed cells from apoptosis induced by ROS.

The activation of TC10, a Rho small GTPase, contributes to v-Rel-mediated transformation

v-Rel is the oncogenic member of the Rel/NF-kappaB family of transcription factors and transforms hematopoietic cells and fibroblasts. Differential display was employed to identify target genes that exhibit altered expression in v-Rel transformed cells. One of the cDNAs identified encodes the chicken ortholog of TC10, a member of the Rho small GTPase family. The expression of TC10 was increased in v-Rel-transformed chicken embryonic fibroblasts (CEFs) 3 to 6-fold relative to control cells at both the RNA and protein levels. An elevated level of active, GTP-bound TC10 was also detected in v-Rel-transformed cells relative to control cells. Expression of a dominant-negative TC10 mutant (TC10T32N) decreased the colony formation potential of v-Rel-transformed cells. Furthermore, overexpression of wild-type TC10 or a gain-of-function mutant (TC10Q76L) greatly enhanced the ability of v-Rel transformed CEFs to form colonies in soft agar. In addition to enhance the transformation potential of v-Rel, the overexpression of wild-type TC10 or the gain-of-function mutant alone enhanced the saturation density of CEFs and was sufficient for their anchorage-independent growth in vitro. These results indicate that elevated TC10 activity contributes to v-Rel-mediated transformation of CEFs and demonstrate for the first time that a Rho factor alone is capable of inducing the in vitro transformation of primary cells.

The suppression of SH3BGRL is important for v-Rel-mediated transformation

The v-rel oncogene is the most efficient transforming member of the Rel/NF-kappaB family of transcription factors. v-Rel induces avian and mammalian lymphoid cell tumors and transforms chicken embryo fibroblasts in culture by the aberrant regulation of genes under the control of Rel/NF-kappaB proteins. Here we report that the expression of SH3BGRL, a member of the SH3BGR (SH3 domain-binding glutamic acid-rich) family of proteins, is downregulated in v-Rel-expressing fibroblasts, lymphoid cells, and splenic tumor cells. Chromatin immunoprecipitation experiments demonstrated that v-Rel binds to the sh3bgrl promoter in transformed cells. Coexpression of SH3BGRL with v-Rel in primary splenic lymphocytes reduced the number of colonies formed by 76%. Mutations in the predicted SH3-binding domain of SH3BGRL abolished the suppressive effect on v-Rel transformation and resulted in colony numbers comparable to those formed by v-Rel alone. However, mutations in the predicted EVH1-binding domain of SH3BGRL only had a modest effect on suppression of v-Rel transformation. This study provides the first example of a gene that is downregulated in v-Rel-expressing cells that also plays a role in v-Rel transformation.

Differential regulation of the inhibitor of apoptosis ch-IAP1 by v-rel and the proto-oncogene c-rel

The v-rel oncogene encoded by reticuloendotheliosis virus is the acutely transforming member of the Rel/NF-kappaB family of transcription factors. v-Rel is a truncated and mutated form of c-Rel and transforms cells by inducing the aberrant expression of genes regulated by Rel/NF-kappaB proteins. The expression of ch-IAP1, a member of the inhibitor-of-apoptosis family, is highly elevated in cells expressing v-Rel and contributes to the immortalization of cells transformed by this oncoprotein. In this study we demonstrate that the elevated expression of ch-IAP1 in v-Rel-expressing cells is due to an increased rate of transcription. The ch-IAP1 promoter was isolated, and four Rel/NF-kappaB binding sites were identified upstream of the transcription start site. Two kappaB sites proximal to the transcription start site were required for v-Rel to activate the ch-IAP1 promoter. While c-Rel also utilized these sites, a third more-distal kappaB site was required for its full activation of the ch-IAP1 promoter. Differences in the transactivation domains of v-Rel and c-Rel are responsible for their different abilities to utilize these sites and account for their differential activation of the ch-IAP1 promoter. Although c-Rel was a more potent activator of the ch-IAP1 promoter than v-Rel in transient reporter assays, cells stably overexpressing c-Rel failed to maintain high levels of ch-IAP1 expression. The reduction of ch-IAP1 expression in these cells correlated with the efficient regulation of c-Rel by IkappaBalpha. The ability of v-Rel to escape IkappaBalpha regulation allows for the gradual and sustained elevation of ch-IAP1 expression directly contributing to the transforming properties of v-Rel.

Mutational analysis of the v-Rel dimerization interface reveals a critical role for v-Rel homodimers in transformation

The v-rel oncogene encoded by reticuloendotheliosis virus strain T is the acutely transforming member of the Rel/NF-kappaB family of transcription factors. In v-Rel-transformed cells, v-Rel exists as homodimers or heterodimers with the endogenous Rel/NF-kappaB proteins c-Rel, NF-kappaB1, NF-kappaB2, and RelA. To examine the contribution of these complexes to v-Rel-mediated transformation, mutations were introduced into the dimerization interface of v-Rel to generate v-Rel mutants with selective dimerization properties. Nine mutants are described in this study that are defective in homodimer and/or heterodimer formation with specific Rel/NF-kappaB family members. Viruses expressing mutants that failed to homodimerize but were able to form heterodimeric complexes were unable to transform splenic lymphocytes in vitro, indicating that the dimerization of v-Rel with endogenously expressed Rel/NF-kappaB proteins is not in itself sufficient for transformation. In addition, two partially transforming mutants were identified that exhibited an impaired ability to form homodimers. Sequence analysis of the proviral DNA from cells transformed by these mutants revealed the presence of multiple secondary mutations in sequences responsible for dimerization and DNA binding. Two of these mutations either enhanced or restored the ability of these proteins to bind DNA as a homodimer. Viruses expressing these proteins transformed cells at levels comparable to or slightly less than v-Rel, suggesting that a threshold level of DNA binding by v-Rel homodimers is required for transformation.

AP-1 factors play an important role in transformation induced by the v-rel oncogene

v-rel is the oncogenic member of the Rel/NF-kappaB family of transcription factors. The mechanism by which v-Rel induces transformation of avian lymphoid cells and fibroblasts is not precisely known. However, most models propose that v-rel disrupts the normal transcriptional regulatory network. In this study we evaluated the role of AP-1 family members in v-Rel-mediated transformation. The overexpression of v-Rel, c-Rel, and c-Rel delta resulted in a prolonged elevation of c-fos and c-jun expression and in a sustained repression of fra-2 at both the mRNA and protein levels in fibroblasts and lymphoid cells. Moreover, the transforming abilities of these Rel proteins correlated with their ability to alter the expression of these AP-1 factors. v-Rel exhibited the most pronounced effect, whereas c-Rel, with poor transforming ability, elicited only moderate changes in AP-1 levels. Furthermore, c-Rel delta, which exhibits enhanced transforming potential relative to c-Rel, induced intermediate changes in AP-1 expression. To directly evaluate the role of AP-1 family members in the v-Rel transformation process, a supjun-1 transdominant mutant was used. The supjun-1 mutant functions as a general inhibitor of AP-1 activity by inhibiting AP-1-mediated transactivation and by reducing AP-1 DNA-binding activity. Coinfection or sequential infection of fibroblasts or lymphoid cells with viruses carrying rel oncogenes and supjun-1 resulted in a reduction of the transformation efficiency of the Rel proteins. The expression of supjun-1 inhibited the ability of v-Rel transformed lymphoid cells and fibroblasts to form colonies in soft agar by over 70%. Furthermore, the expression of supjun-1 strongly interfered with the ability of v-Rel to morphologically transform avian fibroblasts. This is the first report showing that v-Rel might execute its oncogenic potential through modulating the activity of early response genes.

Synergistic stimulation of avian I kappa B alpha transcription by rel and fos/jun factors

Rel/NF-kappa B transcription factors and I Kappa B alpha function in an autoregulatory network. Avian I kappa B alpha transcription is increased in response to both c-Rel and v-Rel. This study shows that I kappa B alpha transcription is synergistically stimulated by Rel and AP-1 factors (c-Fos and c-Jun). However, the response to v-Rel and the AP-1 factors was not as vigorous as that of c-Rel and AP-1. A 386 bp region of the I kappa B alpha promoter (containing two NF-kappa B and one AP-1 binding sites) was shown to be both necessary and sufficient for response to both Rel factors alone or Rel factors in conjunction with the AP-1 proteins. In addition, an imperfect NF-kappa B binding site was found to overlap the AP-1 binding site. Mutation of either of the NF-kappa B binding sites or the AP-1 binding site dramatically decreased the response of the I kappa B alpha promoter to Rel proteins alone or Rel and AP-1 factors. Overexpression of c-Rel or v-Rel resulted in the formation of DNA binding complexes associated with the imperfect NF-kappa B binding site which overlaps the AP-1 site. v-Rel associated with the imperfect NF-kappa B site stronger than c-Rel, and overexpression of v-Rel also resulted in the formation of a v-Rel containing complex bound to a consensus AP-1 site. These studies address the difference in c-Rel and v-Rel's ability to synergistically stimulate I kappa B alpha expression in conjunction with the AP-1 factors.